(60b) Dewatering/Dehydration of Bioethanol Using Ultrasound

Bioethanol production from renewable sources plays an important role in the US effort to facilitate sustainability, mitigate environmental impact, and enhance energy independence. Current technologies used for bioethanol purification include traditional distillation, extractive distillation, azeotropic distillation, and pressure swing distillation, among others. However, each of these has significant limitations, such as high energy consumption and low energy efficiency, inefficient separation, requirements for other chemicals, operational complexity, limited lifetime of materials, etc.

When an ultrasonic wave generated from a piezoelectric actuator is applied to an ethanol-water solution, fine droplets are formed due to capillary wave instability development on the ethanol-water interface and acoustic cavitation. The ethanol concentration in the ultrasound-generated fine droplets is found to be greater than that in the bulk solution, apparently because of an ethanol-enriched shell.

In this study, a batch ultrasonic separation prototype was first developed to determine the feasibility of ultrasound-driven ethanol purification, and the effects of operational parameters, such as liquid temperature, liquid thickness, location of the carrier gas inlet/outlet, and carrier gas flow rate on the enrichment of ethanol in collected mist. Following that, three types of continuous-flow ultrasonic separation prototypes, including a 10-transducer separation unit, were developed to demonstrate the feasibility of replacing the current distillation process. Results from the batch unit show that liquid temperature and carrier gas flow rate significantly affect ethanol concentration in collected mist and the collection rate. A simple process analysis shows that a two-stage continuous-flow ultrasonic separation unit can potentially replace one distillation column in the traditional three-column ethanol purification process, and a five-stage continuous-flow unit could replace two distillation columns in the current process. The ten-transducer separation unit was shown to significantly reduce the effect of carrier flow rate on ethanol enrichment. A preliminary techno-economic analysis shows that this technology has the potential to reduce energy consumption by 30% compared to the current process. The application of ultrasound in ethanol purification may provide an alternative to the current ethanol purification process, operating at atmospheric pressure and at or slightly above ambient temperature.